Update db.py

Ensure directory exists before attempting to write file in db.py

gpt_engineer/db.py

@@ -15,6 +15,9 @@ class DB:
             return f.read()
 
     def __setitem__(self, key, val):
+        # Ensure the directory exists
+        os.makedirs(self.path, exist_ok=True)
+
         with open(self.path / key, 'w', encoding='utf-8') as f:
             f.write(val)